1. Field of the Invention
The present invention relates to a cathode ray tube, and in particular to a glass structure of a cathode ray tube which is capable of improving a deflection efficiency of a cathode ray tube, preventing a BSN phenomenon occurrence and lowering high stress acting on a funnel efficiently while improving the deflection efficiency.
2. Description of the Prior Art
Generally, a BSN (beam shadow neck) means a phenomenon in which a deflected electron beam clashes onto the internal surface of a yoke portion and throws a shadow on a screen.
As depicted in FIG. 1, the conventional color cathode ray tube includes a R (red)•G (green)•B (blue) fluorescent 40 coated onto the internal surface, a panel 10 having an explosion-proof means at the front surface, a funnel 20 welded to the rear end of the panel 10, an electron gun 130 inserted into a neck portion of the funnel 20 and generating an electron beam 60, a deflection yoke 50 for deflecting the electron beam 60, a shadow mask 70 installed to the inner surface of the panel 10 with a certain space and having plural holes for passing the electron beam 60, a mask frame 30 fixedly supporting the shadow mask 70 to make the shadow mask 70 maintain a certain distance from the panel 10, a spring 80 for connecting and supporting the mask frame 30 and the panel 10, an inner shield 90 for shielding the cathode ray tube not to be influenced by outer terrestrial magnetism, and a reinforcing band 110 installed to the circumference of the side surface of the panel 10 and absorbing outer impacts.
A general fabrication process of the conventional color cathode ray tube can be divided into the first half process and the latter half process, and the first half process is coating a fluorescent surface 40 onto the internal surfaces of the panel 10, and the latter half process consists of several processes, that are discussed below.
First, in a sealing process, the panel 10 in which the fluorescent surface is coated and includes a mask assembly is joined to the funnel 20 in which frit is coated onto the sealing surface. Afterward, in an enclosing process, the electron gun 130 is inserted into the neck portion 140 of the funnel 20. And, in an exhausting process the cathode ray tube is sealed after being vacuumized.
Herein, when the cathode ray tube is in the vacuum state, a high tensile force and a high compressive stress act on the panel 10 and the funnel 20.
Accordingly, after the exhausting process, in order to disperse the high stress acting on the front surface of the panel 10, a reinforcing process for adhering the reinforcing band 100 is performed.
An unexplained reference numeral 11 is a funnel body portion, 12 is a funnel yoke portion, 51 is a deflection core, and 52 is a deflection coil.
In the cathode ray tube, because the electron beam 60 reaches the fluorescent 40 coated onto the internal surface of the panel 10, a picture is formed. In order to move the electron beam 60 harmoniously, the internal surface of the cathode ray tube has to be in a vacuum state.
In addition, in order to form a picture on the screen, the electron beam 60 discharged from the cathode of the electron gun 130 has to be deflected while spreading widely on the screen, the deflection yoke 50 consisting of the coil 51 and the core 52 deflects the electron beam.
When a current flows onto the coil 52 of the deflection yoke 50, a magnetic field occurs in the core 51, and the electron beam 60 is deflected while moving along a Z axis by the generated magnetic field.
Herein, a size of the magnetic field is varied according to an amplitude of the current applied to the coil 52.
Generally, a deflection angle and a deflection center of the electron beam 60 is determined according to a size, a shape, a position of the coil 52 and the core 51 of the deflection yoke 50.
In addition, according to intensification of electronic appliance power consumption regulations, attempts to lower the power consumption of electronic appliances have been made. As well as other electronic appliances, lowering power consumption is an essential particular in the cathode ray tube.
In order to slim down the cathode ray tube and reduce power consumption thereof, a current applied to the deflection yoke 50 has to be decreased.
However, when the applied current is reduced, because the magnetic field generated in the core 51 is weakened, a sufficient deflection angle can not be secured, and accordingly a picture can not be formed.
In addition, when an absolute quantity of the core 51 and the coil 52 of the deflection yoke 50 is increased, a material cost and an absolute quantity of a leakage magnetic field are increased, and accordingly it is not good in the product reliability aspect.
Accordingly, because slimming down and reducing the power consumption of the cathode ray tube are greatly related to the deflection efficiency of the deflection yoke 50, improving the efficiency of the deflection yoke 50 is efficient way to slim down the cathode ray tube and reduce the power consumption thereof.
There are methods for improving the deflection efficiency. A first method is changing a section shape of the funnel yoke portion 12 and the coil 52 from a circular shape to a square shape. In the first method, because a distance between the electron beam 60 and the deflection yoke 50 is reduced, the electron beam 60 can be easily deflected by a smaller deflection magnetic field.
A second method is placing the core 51 and the coil 52 of the deflection yoke 50 at the neck portion 13 of the funnel 20.
In the second method, as depicted in FIG. 2, when the position of the deflection yoke 50 is changed so as to get closer to the neck portion 13 of the funnel 20, a distance D (before the change) between the deflection yoke 50 and the electron beam 60 is shorter than a distance d (after the change). Accordingly, the electron beam 60 crashes onto the internal surface of the funnel 20 at the is overlap portion.
In more detail, when the deflection center is moved toward the neck portion 13, a distance between the electron beam 60 and the deflection yoke 50 is reduced, the electron beam 60 can be influenced by a larger deflection magnetic field.
Because a distance between the electron beam 60 and the yoke portion 12 of the funnel 20 is smaller, the electron beam 60 crashes onto the internal surface of the yoke portion 12 and throws a shadow on the screen.
The section of the funnel yoke portion 12 is getting smaller toward the neck portion 13 of the funnel yoke portion 12, by reducing a distance between the electron beam 60 and the deflection yoke 50, a deflection efficiency can be improved.
The position change means moving the deflection center toward the neck portion 13, and accordingly the electron beam 60 is deflected early by the magnetic field.
In addition, third method is converting an electron beam scanning type from a horizontal scanning type into a vertical scanning type.
Generally, the cathode ray tube has a ratio of horizontal length:vertical length as 4:3 or 16:9. In the horizontal scanning type, 4, 16 distance has to be deflected. But, in the vertical scanning type, merely 3, 9 distance has to be deflected, a deflection electric power for the same deflection is smaller than that of the horizontal scanning type.
FIG. 3 illustrates a BSN phenomenon occurring at the yoke portion 12 of the funnel 20 of the cathode ray tube in applying of the vertical scanning type. As depicted in FIG. 3, the BSN phenomenon is caused by the electron gun arranged in the vertical scanning type and mainly occurs along the long side portion and the diagonal portion of the yoke portion 12.
Recently, in practical use, all three methods have been combined to improve the deflection efficiency, the improvement of the deflection efficiency makes possible to slim down the cathode ray tube and reduce a power consumption thereof.
In the meantime, FIG. 4 illustrates a BSN phenomenon that occurs by the electron beam 60 crashing onto the internal surface of the yoke portion 12 of the funnel 20 according to the deflection efficiency improvement in applying of the three methods.
In more detail, the lower the deflection efficiency, the more a BSN phenomenon occurrence portion moves toward a TOP (top of round), the higher the deflection efficiency, the more a BSN phenomenon occurrence portion moves toward a NSL (neck seal line).
Accordingly, a BSN phenomenon occurrence between a RL (reference line) and the NSL (neck seal line) is inevitable.
The BSN phenomenon occurrence according to the deflection efficiency increase is a major problem in slimming down the cathode ray tube and reducing a power consumption thereof.
However, the methods for improving the deflection efficiency increase the BSN phenomenon occurrence according to the electron beam deflection. The BSN phenomenon means a phenomenon in which a shadow of the internal surface of the yoke portion 12 is thrown onto the screen, it is very important characteristic in fabricating of the cathode ray tube.
In recent years, to improve the deflection efficiency of the cathode ray tube, a funnel having a square-shaped yoke portion and the vertical scanning type are applied to the cathode ray tube, however, those applications cause more BSN phenomenon occurrence than that in application of a funnel having the conventional circular shaped yoke portion and the horizontal scanning type.
In more detail, in application of the funnel having a square-shaped yoke portion, a distance between the electron beam 60 and the yoke portion 12 is reduced. In moving of the deflection center toward the neck portion 13, because a deflection angle of the electron beam 60 is increased and the electron beam 60 moves toward the internal surface of the yoke portion 13, the BSN phenomenon occurrence is increased, and accordingly a reliability of the cathode ray tube may be lowered.
In addition, in the vertical scanning type cathode ray tube, each R, G, B cathode emitting the electron beam 60 from the electron gun 130 has to be placed so as to be parallel to the vertical axial line. Herein, the electron beam emitted from the R, B cathodes is placed apart a certain distance from the Z axis in the vertical direction in comparison with the G electron beam.
Herein, because the electron beam emitted from the R, B cathodes gets closer to the deflection magnetic field as the distance separated from the Z axis, the electron beam 60 is deflected toward the vertical direction and crashes onto the internal surface of the long side of the funnel yoke portion 12, and accordingly the BSN phenomenon occurs.
The above-mentioned phenomenon greatly occurs between the funnel yoke portion 12, the RL (reference line) and the NSL (neckline seal line).
In the slim and the vertical scanning type cathode ray tube, the BSN phenomenon occurs along the diagonal portion and the long side portion, most of all, it mainly occurs at the long side's internal surface around the diagonal portion of the funnel yoke portion 12.
Herein, when the funnel yoke portion 12 is moved to the direction perpendicular to the Z axis (central axis), namely, gets farther apart, the BSN phenomenon is reduced, however, the deflection efficiency is lowered, and accordingly it is impossible to slim down the cathode ray tube and reduce power consumption thereof.
In the meantime, in the present display market, slimming down a display's volume is essential to facilitate a secure installation space. For example, a LCD (liquid crystal display) and a PDP, etc. are typical slim displays. In comparison with them, the cathode ray tube is heavy and large, and it is in a disadvantageous position in the installation facilitation, and accordingly it is required to slim down.
With the trend, in order to slim down the cathode ray tube, it is essential to secure the deflection angle, for that, the yoke portion 12 has the square shape, however, because it is an unstable shape in the structural aspect, a high stress acts on the panel 10 and the funnel 20.
FIG. 5 is a schematic view illustrating a stress distribution on the yoke portion 12 of the funnel 20. As depicted in FIG. 5, by reducing the total length of the funnel 20 to slim down the cathode ray tube, a stress acts on the yoke portion 12 of the cathode ray tube. In FIG. 5, a dotted line arrow mark is a compression stress, a solid line arrow mark is a tensile stress. Herein, in the funnel 20 made of glass, the intensified stress distribution can be a fetal problem.
In more detail, when the funnel yoke portion 12 has the square shape, because the tensile stress on the outer surface of diagonal portion of the yoke portion 12 is increased, a high stress problem on the glass has to be solved.
In other words, when the cathode ray tube is slimmed down, the total length of the funnel 20 is shortened. In addition, when the yoke portion 12 has a square shape, a stress on the yoke portion 12 is increased, a deflection angle of the electron beam 60 of the electron gun to the fluorescent 40 is increased, and accordingly the BSN phenomenon occurs. In that case, a shadow is thrown around the fluorescent, and it may lower the reliability of the cathode ray tube.